Site Balancing Of A Large Flexible Rotor Containing Unbalance Eccentricity And Permanent Residual Bow

Abstract

When turbine-generators operating at constant speed require site trim balancing, this is most commonly performed at the synchronous speed using a conventional influence coefficient method. In some cases, the vibration of flexible rotors during run-up through critical speeds is excessive and balance can only be achieved by correcting in tum each model defect throughout the speed range. Difficulties arise in the case of rotors that contain a permanent residual bow. Classical phase/speed relationships through a critical speed no longer apply and conventional balancing techniques are invalid. The theoretical explanation of the unbalance response of bowed flexible rotors has recently been well documented. This paper describes how a flexible rotor containing a significant bend was optimally balanced over its complete speed range, by incorporating bowed rotor response theory into the balance technique.